Conventionally, as an imaging element (image sensor), there is mainly used a semiconductor element having a structure of a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). Also, there is recently proposed an imaging element including an organic photoelectric conversion element having a photoelectric conversion layer formed with an organic semiconductor material (for example, see Patent Literatures 1 to 3). The organic photoelectric conversion element does not need to contain a color filter, and can have a structure and a manufacturing process which are simpler than those of the conventional inorganic semiconductor element.
The conventional organic photoelectric conversion element as described in Patent Literatures 1 to 3 has a configuration in which an organic photoelectric conversion portion is disposed between a pair of electrodes. For example, a lower electrode, an organic photoelectric conversion portion, and an upper electrode are laminated in this order on a substrate. Also, the conventional organic photoelectric conversion element includes various intermediate layers such as an electron blocking layer, a buffer layer and an active layer, between the organic photoelectric conversion portion and each electrode in some cases.